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953 nut

Safety Switches 101

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953 nut

Frequently we field questions about safety switches and many times the answers given may or may not be correct for the particular Wheel Horse we are talking about. For accurate information it is best to refer to the “Demystification Guide” or electrical drawings for the specific model and year tractor. There is no one size fits all answer, I will attempt to provide a little food for thought and some general information on the subject.

First, we need to understand how various switches receive their names. The switches used in safety systems are momentary switches, if no force is applied to them, they return to their “Normal” position. That would be the same condition (open or closed) that they had when they were on the shelf ready to be installed. Some will be NO (normally open) and some will be NC (normally closed). In the case of PTO switches there are two switches ganged together.

The seat switch and half of the PTO switch are used in the ignition circuit. The second half of the PTO switch is in the starter circuit.

As an example, the Seat and PTO safety switches for a Magneto or Trigger Ignition system are designed to ground out the magneto if the PTO is engaged and there is no driver in the seat. These switches are in series. The seat switch is a N.C. (normally closed) switch which opens when weight is placed on the seat. The half of the PTO switch that is in the ignition circuit is N.O. (normally open) which is open when disengaged and will close when engaged. With the PTO switch closed and no weight in the seat the magneto will be grounded and the engine will stop running. With the PTO disengaged the seat switch will have no effect.

If the tractor has a Battery Ignition system the PTO and Seat safety switches are wired to interrupt the power from the ignition switch to the ignition coil when the PTO is engaged and there is no driver in the seat. These switches are in parallel. The seat switch is a N.O. (normally open) switch and will close when weight is on the seat. The half of the PTO switch that is used for ignition is N.C. (normally closed) and opens when the PTO is engaged. Both of these switches receive power from the ignition switch “I” terminal and either one being closed will pass the power on to the ignition coil. If the PTO is engaged that switch will open, as long as there is weight in the seat the engine will continue to run because the Seat switch will be closed. If the weight is removed from the seat while the PTO is engaged the engine will stop. If the PTO is disengaged the seat switch has no effect.

Looking at the drawings below should clarify this muddy issue.

690491981_magnetoignitionsafetyswitches.jpg.5caab5dc3fca5be3804276bd12b9351c.jpg

 

Edited by 953 nut
fat finger
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ebinmaine

Might want to "pin" this to the top of Electrical.

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CCW

This begs the question.  How do we know if we have a magneto ignition or battery ignition system?

Edited by CCW

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Pullstart
1 hour ago, CCW said:

This begs the question.  How do we know if we have a magneto ignition or battery ignition system?

 

Battery ignition will have points and condenser, with external coil.  :handgestures-thumbupright:

 

@953 nut that is a little excerpt of the wiring gospel right there!

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953 nut
3 hours ago, CCW said:

This begs the question.  How do we know if we have a magneto ignition or battery ignition system?

The Kohler engine manual has all the information you will need. If your engine has a spark plug wire coming out of the flywheel cover it is a magneto ignition. If it has the triangular breakerless ignition treat it as a magneto.

image.png.c03e5d815909525f89f8f15dbe6f87dd.png

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oliver2-44

Thanks 953, Very useful information.  I agree this should be pinned.

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BOB ELLISON

Very nice diagram Richard .

Good information  to know

Edited by BOB ELLISON
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SylvanLakeWH

Read it twice...

Head hurts...

First time it made sense to me...

Thanks!!!

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BPC23
On 3/6/2020 at 6:03 AM, SylvanLakeWH said:

Read it twice...

Head hurts...

First time it made sense to me...

Thanks!!!

 

Passing time during quarantine,

Read post reminiscent of haiku,

Made me smile.

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ebinmaine
Just now, BPC23 said:

 

Passing time during quarantine,

Read post reminiscent of haiku,

Made me smile.

AWESOME.

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SylvanLakeWH

I once knew haiku

then quarantine made me red

now spring brings wheel horse tractors

 

 

Couldn't resist... 5,7,5... :hide:

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BPC23

Very well done, Jim!

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Goldnboy

 For battery ignition  systems I have always  wired these switches in the circuit  from "S" on the key to the solenoid "S" terminal. 

What is the difference between  the methods?

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